Smoothing device

ABSTRACT

A smoothing device of a press arrangement for dewatering a fibrous web in a machine for producing or finishing the fibrous web including a rough belt, a smooth belt and a smoothing element. The rough belt being endless and water-absorbing. The rough belt arranged on a side of the fibrous web. The smooth belt is endless and arranged on an opposite side of the fibrous web. The rough belt, the fibrous web and the smooth belt running through a press nip together and the rough belt is led away from the fibrous web after passing through the press nip. The smoothing element forms a smoothing nip with the smooth belt after the rough belt is led away from the fibrous web, the smoothing element having a smooth pressing surface.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application No. PCT/EP03/01315, entitled“SMOOTHING DEVICE”, filed Feb. 11, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a smoothing device for a pressarrangement for dewatering a paper, board, tissue or other fibrous webin a machine for producing and/or finishing the same.

2. Description of the Related Art

Press arrangements lead to pronounced two-sidedness of the fibrous webwith regard to smoothness, since the smooth belt smoothes the fibrousweb while the other belt, because of the necessary porosity in order toensure the water absorption capability, has a certain surface roughnessand therefore roughens the fibrous web. However, the smooth beltprovides advantages in guiding the fibrous web, so that omitting thelatter would not be desired.

What is needed in the art is, an apparatus to reduce the two-sidednessof the fibrous web in the simplest possible way.

SUMMARY OF THE INVENTION

According to the present invention, a smooth belt forms a smoothing nipwith a smoothing element having a smooth pressing surface after therough belt is led away. This smoothing nip increases the smoothness onboth sides of the fibrous web while reducing the two-sidedness withminimum expenditure. The smoothing element simultaneously guides thefibrous web after the smoothing nip, that is to say that the smoothingbelt transfers the fibrous web to the smoothing element.

In order to assist the transfer of the fibrous web, the surface of thesmooth belt is softer than that of the smoothing element.

In order to make it possible to discharge broke into the machinebasement, it is advantageous if the smoothing element and/or the smoothbelt are arranged such that they can be moved away from each other and,as a result, a discharge gap is implemented.

Since the fibrous web is still relatively moist in the region of thepress arrangement, it is sufficient, for the purpose of smoothing, ifthe smooth belt and the smoothing element are pressed against each otherwith a contact force which is between 3 kN/m and 100 kN/m, preferablybetween 5 kN/m and 20 kN/m. For the purpose of optimization, in theinterests of the lowest possible two-sidedness of the fibrous web, it isadvantageous if the smooth belt and the smoothing element are pressedagainst each other with a contact force which is set or controlled as afunction of the level of two-sidedness of the fibrous web after thesmoothing device, preferably at the end of the machine.

In this case, the smoothing element is formed as a smooth, endlesslycirculating smoothing belt or else as a smooth, rotatable smoothingroll. In the case of the smoothing roll, for the purpose of drying andfor the purpose of increasing the smoothness of the rough side of thefibrous web, it is advantageous if the smoothing roll is heated and, inparticular, is formed as a drying cylinder.

Because of the low accumulation of water in the press nip, smooth beltsare preferably used at the end of the press section. This means that thepress nip should preferably be the last press nip of the machine.

In order to improve the guidance of the fibrous web, particularly athigh speeds, in particular if the fibrous web is transferred from thesmoothing element to a drying group for drying the fibrous web, thetransfer should be assisted by at least one suction device. However, itcan also be advantageous if the fibrous web runs from the smoothingelement to a following element with a short free draw, that is to say ashort unsupported distance. In the drying group, the fibrous web issupported by a drying fabric, and is led alternately over heated dryingcylinders and guide rolls. The drying cylinders are arranged under thefibrous web in order to improve the web guidance, to simplify theconstruction and to permit simple discharge of broke.

If the smooth belt runs above the fibrous web, then the fibrous web canbe transferred in a secure and simple way from the smoothing element toa drying fabric of a following drying group. The drying fabric is ledpast a suction device, preferably in the form of a suction box, in thetransfer region. However, somewhat better web guidance results if thesmooth belt runs under the fibrous web. In this case, the fibrous web issimply transferred from the smoothing element to a transfer suctionroll. The suction roll then, in turn, transfers the fibrous web to thedrying fabric of the drying group. However, it is also possible for thefibrous web to be transferred from the smoothing element to anair-permeable transfer belt which, in the transfer region, wraps arounda suction device. The suction device being in the form of a suctionroll, and it transfers the fibrous web to the drying fabric of thefollowing drying group.

In a development of the invention, provision is made for a suctiondevice for attracting the fibrous web by suction that is arrangeddownstream of the smoothing element in the running direction of thefibrous web. In this case, the arrangement of the suction device isindependent of the conveying mechanism onto which the fibrous web istransferred. Thus, the fibrous web can be transferred, for example, ontoa transfer belt or directly onto a drying fabric. By way of the suctiondevice, the fibrous web is detached from the preceding smoothingelement, in particular a smoothing roll, under a defined suction force.Web flutter and breaks, such as can occur in the case of an open drawwithout support by a suction device, are thereby avoided. The suctiondevice is preferably configured in such a way that it includes a suctionbox and/or a suction roll. The suction roll is preferably equipped onits circumferential surface with a helical or spiral groove, in whichholes for extracting air and water are made at fixed intervals. For thispurpose the perforated roll shell is connected to a vacuum source. Thesuction box is preferably configured in such a way that it immediatelyadjoins an unwrapped region of the circumferential surface of thesuction roll. In a particular refinement, the suction box has a firstand a second element that is pressed resiliently against the fibrousweb, between which, at least one suction zone, for attracting thefibrous web by suction, is formed. In one embodiment of the presentinvention, provision is made for a plurality of zones to be evacuatedwith different pressures to be arranged after and/or beside one anotherin the region of the suction box. In this manner the desired suctionpressure can be set very precisely and in accordance with the web speedand other web parameters. Here, it also proves to be advantageous if thecontact pressure of at least one of the two elements can be set.

In another embodiment of the present invention, provision is made for itto be possible for the fibrous web, after being transported past thesuction device, to be conveyed over a drying cylinder and at least onefurther suction device.

The present invention is also suitable for use when threading a strip ofa fibrous web. For this purpose, it is sufficient, for example, if thesuction roll is evacuated only in a section over which the threadingstrip is guided. In this case, if a suction box is also present, thelatter does not necessarily have to be evacuated. However, the suctionbox can also be evacuated in accordance with the width of the evacuatedsection of the suction roll. Using this method for threading the startof a fibrous web, it is possible to lead the web on without a rope. Thestrip can be expanded to the full width of the fibrous web with the aidof a couching device, the suction roll and/or the suction box then beingevacuated over the full width of the fibrous web.

The drying fabric is brought into contact with the smoothing roll. Forthis purpose, the suction roll and the suction box are arranged suchthat it can be pivoted.

In a further embodiment of the present invention, the drying fabric isdriven at a somewhat higher speed than the belt of the press section. Inthis way, the fibrous web can be detached more easily from the smoothingelement, in particular the smoothing roll. In addition, thetechnological paper properties of the web, in the web running direction,are influenced positively as a result. A speed difference of between0.5% and 5.0% is preferred.

With the present invention, closed web guidance from the wet end as faras the drying section is implemented and web flutter and web breaks ofthe fibrous web are avoided. The press arrangement ensures lowtwo-sidedness of the web with respect to the smoothness with asimultaneously very high level of smoothness and reliable web threading.This is based on the fact that the fibrous web has no, or only a short,free draw region, that is to say a region in which it is not supported.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 shows a schematic side view of a press arrangement with asmoothing device of an embodiment of the present invention;

FIG. 2 shows a press arrangement with another embodiment of a smoothingdevice;

FIG. 3 shows a schematic side view of another embodiment of a pressarrangement with a smoothing device;

FIG. 4 shows a further schematic view of another embodiment of a pressarrangement with a smoothing device; and

FIG. 5 shows a suction roll in conjunction with a suction box in anenlarged illustration of the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate one preferred embodiment of the invention, in one form, andsuch exemplifications are not to be construed as limiting the scope ofthe invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

In every case, fibrous webs 1, 20 and 53 are led through a press niptogether with an endlessly circulating, water-absorbing, relativelyrough belt 2 or 24 in the form of a press felt and a likewise endlesslycirculating, smooth belt 3 and 25 arranged on the opposite side offibrous webs 1, 20 or 53. In at least one case, the press nip is thelast or even the only press nip of a press section of a papermakingmachine for dewatering fibrous web 1, 20 and 53 and is generally formedby two press rolls 12 or 31 and 32 pressed against each other. In thepress nip, only relatively little water is pressed out of fibrous web 1,20 or 53, so that only one press felt is sufficient to pick up the waterpressed therefrom. Smooth belt 3 or 25 improves the guidance of fibrousweb 1, 20 or 53, in particular at high machine speeds. The two belts 2and 3 or 24 and 25 are respectively led over guide rolls 9 or 26 outsidethe press nip.

From the press section, fibrous web 1, 20 or 53 is led to a drying groupof the papermaking machine. There, fibrous web 1, 20 and 53 is supportedby a drying fabric 5 or 38, and is led alternately over heated dryingcylinders 10, 41 and 51 and evacuated guide rolls 11 and 42. Dryingcylinders 10, 41 and 51 are arranged under and guide rolls 11 and 42 arearranged above fibrous web 1, 20 or 53. The meandering run of fibrousweb 1, 20 or 53 results in a simple and space-saving construction of thedrying group. In addition, drying groups of this type are highlysuitable for high machine speeds and have fast and reliable discharge ofbroke.

In the press nip fibrous web 1, 20 and 53 is smoothed on one side as aresult of the contact with smooth belt 3 or 25, while the other sideremains rough or even becomes rougher as a result of the contact withthe relatively rough press felt. Although this two-sidedness can bereduced in the calendaring units, arranged at the end of the machine, itcan seldom be entirely corrected.

After the press nip, however, fibrous web 1, 20 and 53 is stillrelatively moist, so that the two-sidedness can be influenced withrelatively simple means and low pressing forces. For this purpose, thepress felt is led away from fibrous web 1, 20 and 53 after the pressnip. Fibrous web 1, 20 or 53 can then run through a smoothing device, inwhich the two-sidedness of the fibrous web 1, 20 and 53 is counteractedby smoothing. There then follows the transfer of fibrous web 1, 20 or 53to a respective drying fabric 5 or 38 of the following drying group.

The smoothing device is formed by a smoothing roll 4, 34 or 50, which ispressed against smooth belt 3, 25 with fibrous web 1, 20 or 53therebetween. In this case, smooth belts 3 and 25 are respectively,supported by a press roll 13 and 35 on the opposite side of the fibrousweb. The position of smoothing roll 4, 34 or 50 can be changed in such away that the smoothing nip can also be opened in order to dischargebroke. Of course, it is also possible to arrange press roll 13 or 35 tobe displaceable. Furthermore, smoothing roll 4, 34 or 50 can also bereplaced by a smoothing belt, which is forced toward smooth belt 3 or 25by a roll or likewise wraps around press roll 13 or 35 with smooth belt3 or 25.

In the press arrangements that are illustrated in FIGS. 1 and 2, smoothbelt 3 runs under fibrous web 1, which offers advantages in the guidanceof the web.

In FIG. 1, following the smoothing operation, fibrous web 1 istransferred from smoothing roll 4 to a transfer belt 14, which, in turn,passes on fibrous web 1 to drying fabric 5. Transfer belt 14 isassociated with two transfer points, transfer belt 14, wrapping around aroll 8. The roll associated with smoothing roll 4 is designed as asuction roll 7 in order to assist the transfer.

According to FIG. 2, fibrous web 1 is transferred to transfer suctionroll 7 then to drying fabric 5. In contrast to this, smooth belt 3 inthe press arrangement shown in FIG. 3 is arranged above fibrous web 1.This simplifies the transfer of fibrous web 1 after smoothing, sincefibrous web 1 can be transferred from smoothing roll 4 to drying fabric5 directly, that is to say without being turned. In order to assist thetransfer, drying fabric 5 runs on a suction box 6 in the region of thetransfer. The vacuum originating from suction box 6 pulls fibrous web 1toward drying fabric 5.

A fibrous web 20 as illustrated in FIG. 4 is transported in thedirection of an arrow A by transport belts 21-25, each of which run overguide rolls 26. At the transfer points between transport belts 21-25there are suction rolls with stationary suction boxes and a roll shellthat rotates therearound, such as suction rolls 27 and 28 with suctionboxes 29 and 30, respectively.

Between press rolls 31 and 32, of which the lower is equipped with apressing element 33, fibrous web 20 is led to a pair of smoothing rolls34 and 35. Smoothing roll 34 is additionally equipped with doctors 36and 37 for removing contaminants.

From transport belt 25, fibrous web 20 is transferred onto drying fabric38. For this purpose, use is made of suction roll 39 in conjunction withsuction box 40, which is illustrated above suction roll 39 and, in oneembodiment, has an approximately trapezoidal cross section. As a resultof the arrangement of suction box 40 and of suction roll 39, fibrous web20 is transferred without a free draw directly from contact withsmoothing roll 34 onto a suction region on the side facing suction roll34. Drying fabric 38 is rotated at a speed of 0.5 to 5.0% faster thantransport belts 21-25.

Fibrous web 20 is then led onward over drying cylinder 41 and from thereto a further combination of suction roll 42 and suction box 43.

FIG. 5 shows a suction box 52 arranged between a smoothing roll 50 and adrying cylinder 51 or between two drying cylinders 50 and 51 in order toattract, by suction, fibrous web 53 (shown on only one side here forreasons of simplification) from smoothing roll 50 and to transfer it todrying cylinder 51. Fibrous web 20 is led around suction roll 54underneath suction box 52. In order to attract fibrous web 20 bysuction, suction box 52 is equipped with a suction region 57 bounded byspringy elements 55 and 56 and having an outlet 58 for the discharge ofextracted air and moisture. Elements 55 and 56 can be actuated byadjusting shafts 59 and 60 respectively in order to change their contactpressure against fibrous web 53. Suction region 57 can be followed byfurther suction regions, which, just like suction region 57, are boundedby resilient elements. It is possible for the suction force to bechanged individually in each of the suction regions in order to achieveoptimum transfer of fibrous web 53 to drying cylinder 51.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. A smoothing device of a press arrangement for dewatering a fibrousweb in a machine for one of producing and finishing the fibrous web,comprising: a rough belt being endless and water-absorbing, said roughbelt arranged on a side of the fibrous web; a smooth belt being endlessand arranged on an opposite side of the fibrous web, said rough belt,the fibrous web and said smooth belt running through a press niptogether, said rough belt being led away from the fibrous web afterpassing through said press nip; and a smoothing element forming asmoothing nip with said smooth belt after said rough belt is led awayfrom the fibrous web, said smoothing element having a smooth pressingsurface.
 2. The smoothing device of claim 1, wherein said smooth belttransfers the fibrous web to said smoothing element.
 3. The smoothingdevice of claim 1, wherein at least one of said smoothing element andsaid smooth belt are arranged so that they move from each other.
 4. Thesmoothing device of claim 1, wherein said smooth belt has a firstsoftness and said smoothing element has a second softness, said firstsoftness greater than said second softness.
 5. The smoothing device ofclaim 1, wherein said smooth belt and said smoothing element are pressedwith a contact force of between approximately 3 kN/m and 100 kN/m. 6.The smoothing device of claim 5, wherein said contact force is betweenapproximately 5 kN/m and 20 kN/m.
 7. The smoothing device of claim 1,wherein said smooth belt and said smoothing element are pressed with acontact force which is one of set and controlled as a function of alevel of two-sidedness of the fibrous web after the smoothing device. 8.The smoothing device of claim 1, wherein said smooth belt and saidsmoothing element are pressed with a contact force which is one of setand controlled as a function of a level of two-sidedness of the fibrousweb after the machine.
 9. The smoothing device of claim 1, wherein saidsmoothing element is a smoothing belt that is endless and circulating.10. The smoothing device of claim 1, wherein said smoothing element is asmooth, rotatable smoothing roll.
 11. The smoothing device of claim 10,wherein said smoothing roll is heated.
 12. The smoothing device of claim1, wherein said press nip is the last press nip of a plurality of pressnips of the machine.
 13. The smoothing device of claim 1, furthercomprising a drying group for drying the fibrous web, the fibrous webbeing transferred from said smoothing element to said drying group in atransfer region.
 14. The smoothing device of claim 13, furthercomprising at least one suction device, the fibrous web beingtransferred in said transfer region with the assistance of said at leastone suction device.
 15. The smoothing device of claim 13, wherein saiddrying group further includes: a drying fabric supporting the fibrousweb; a plurality of drying cylinders; a plurality of guide rolls, saiddrying fabric supporting the fibrous web being alternately guided overone of said plurality of drying cylinders and one of said plurality ofguide rolls.
 16. The smoothing device of claim 15, wherein saidplurality of drying cylinders are arranged under the fibrous web. 17.The smoothing device of claim 1, wherein said smooth belt runs above thefibrous web.
 18. The smoothing device of claim 15, further comprising asuction device, the fibrous web being transferred to said drying fabricfrom said smoothing element in said transfer region, said suction devicebeing proximate to said drying fabric in said transfer region.
 19. Thesmoothing device of claim 18, wherein said suction device is a suctionbox.
 20. The smoothing device of claim 15, wherein said smooth belt runsunder the fibrous web.
 21. The smoothing device of claim 20, furthercomprising a transfer suction roll, the fibrous web being transferredfrom said smoothing element to said transfer suction roll, the fibrousweb then being transferred from said transfer suction roll to saiddrying fabric.
 22. The smoothing device of claim 20, further comprising:a suction device; and an air permeable transfer belt wrapping aroundsaid suction device, the fibrous web being transferred from saidsmoothing element to said air permeable transfer belt, said airpermeable transfer belt then transferring the fibrous web to said dryingfabric.
 23. The smoothing device of claim 22, wherein said suctiondevice is a suction roll.
 24. The smoothing device of claim 1, furthercomprising a suction device for attracting the fibrous web by suction,said suction device being arranged downstream of said smoothing elementin a running direction of the fibrous web.
 25. The smoothing device ofclaim 24, wherein said suction device includes at least one of a suctionbox and a suction roll.
 26. The smoothing device of claim 25, whereinsaid suction box is arranged directly on an unwrapped region of acircumferential surface of said suction roll.
 27. The smoothing deviceof claim 25, wherein said suction box includes a first element and asecond element each of which are pressed resiliently against the fibrousweb with a contact force, a zone between said first element and saidsecond element being a suction zone for attracting the fibrous web bysuction.
 28. The smoothing device of claim 27, wherein said contactforce of at least one of said first element and said second element isset to a predetermined value.
 29. The smoothing device of claim 24,further comprising a transfer belt, the fibrous web being transferredfrom said smoothing element to said transfer belt.
 30. The smoothingdevice of claim 24, further comprising a drying fabric, the fibrous webbeing transferred from said smoothing element to said drying fabric. 31.The smoothing device of claim 24, further comprising: at least onefurther suction device; and a drying cylinder, the fibrous web afterbeing transported past said suction device is conveyed over said dryingcylinder and said at least one further suction device.
 32. The smoothingdevice of claim 25, wherein the fibrous web includes a threading stripassociated with the fibrous web, at least one of said suction roll andsaid suction box including a region being separately evacuateable, saidregion corresponding to a width of said threading strip during thethreading of the fibrous web.
 33. The smoothing device of claim 25,wherein at least one of said suction roll and said suction box is one ofset on and off said smoothing element.
 34. A method of threading a stripof a fibrous web in a papermaking machine, comprising the step ofapplying a vacuum to the strip in a region proximate to one of a suctionroll and a suction box.
 35. The method of claim 34, further comprisingthe step of completing a threading operation, said completing athreading operation including the steps of: bringing the strip to a fullwidth of the fibrous web by way of a couching device; and contacting adrying fabric with a smoothing roll.